In general, acrylic acid is produced by a two-stage oxidation reaction process which comprises a contact reaction of propylene and oxygen in the presence of a catalyst to produce acrolein, and then a contact reaction of the resultant acrolein and oxygen. Recently, however, processes for producing acrylic acid in one stage using propane as a starting material are being investigated, and many proposals have been made on catalysts for use therein. Representative examples thereof include metal oxide catalysts such as an [Mo, Te, V, Nb] system (patent document 1) and [Mo, Sb, V, Nb] systems (patent documents 2 and 3).
Furthermore, some patent applications were recently filed with respect to processes for producing a catalyst having improved performances as compared with those metal oxide catalysts. For examples, patent document 4 discloses a process for producing a catalyst which comprises reacting a molybdenum compound, a vanadium compound, and an antimony compound in an aqueous medium at 70° C. or higher, mixing the resultant aqueous reaction solution with a niobium compound, subsequently vaporizing the resultant mixture to dryness, and calcining the solid matter at a high temperature.
Patent document 5 discloses a method of catalyst modification which comprises impregnating an [Mo, Te, V] catalyst or an [Mo, Sb, V] catalyst with a solution containing one or more elements selected from the group consisting of W, Mo, Cr, Zr, Ti, Nb, Ta, V, B, Bi, Te, Pd, Co, Ni, Fe, P, Si, rare-earth elements, alkali metals, and alkaline earth metals to thereby deposit other metal(s) on the catalyst. The catalytic performances of the modified catalyst in the ammoxidation reaction of propane are evaluated therein.    Patent Document 1: JP-A-7-010801 (claims)    Patent Document 2: JP-A-9-316023 (claims)    Patent Document 3: JP-A-10-036311 (claims)    Patent Document 4: JP-A-10-137585 (claims)    Patent Document 5: JP-A-10-28862 (claims)